Abstract:

A cutting tool insert includes a body of cemented carbide, cermet,
ceramics, cubic boron nitride based material or high speed steel and a
hard and wear resistant coating including at least one metal nitride
layer. The coating includes at least one layer of a thermally stabilized
cubic structured (Ti1-(x+z)SixMez)N phase with
0.04<x<0.20 and 0<z<0.10, with a constant elemental
composition throughout the layer where Me is one or more of the metal
elements Y, Hf, Nb, Ta, Mo, W, Mn, Fe and Zn with a thickness of 0.5 to
10 μm. The layer is deposited using cathodic arc evaporation and is
particularly useful for machining of stainless steel and super alloys.

Claims:

1. Cutting tool insert comprising a body of cemented carbide, cermet,
ceramics, cubic boron nitride based material or high speed steel and a
hard and wear resistant coating comprising at least one metal nitride
layer characterised in that said layer is a cubic structured
(Ti1-(x+z)SixMez)N with 0.04<x<0.20, preferably
0.06<x<0.12 and 0<z<0.10, preferably 0.005<z<0.05 with
a constant elemental composition throughout the layer, where Me is one or
more of the metal elements Y, Hf, Nb, Ta, Mo, W, Mn, Fe and Zn,
preferably Y, Nb, Mo and Fe with a layer thickness of 0.5 to 10 μm,
preferably 0.5 to 5 μm.

2. Cutting tool insert according to claim 1 characterised in that said
layer has a hardness at room temperature of 28<H<44, preferably
33<H<40 GPa.

3. Cutting tool insert according to claim 1 characterised in that said
layer has a compressive stress level of -6.0<σ<-0.5 GPa,
preferably of -4.0<σ<-1.0 GPa.

4. Cutting tool insert according to claim 1 characterised in that said
layer has been deposited with PVD, preferably cathodic arc evaporation.

5. Cutting tool insert according to claim 1 characterised in that said
body is coated with an inner single- and/or multilayer coating of, e.g.,
TiN, TiC, Ti(C,N) or (Ti,Al)N, preferably (Ti,Al)N and/or an outer
single- and/or multilayer coating of, e.g., TiN, TiC, Ti(C,N) or
(Ti,Al)N, preferably (Ti,Al)N, to a total coating thickness of 1 to 20
μm, preferably 1 to 10 μm and most preferably 2 to 7 μm
according to prior art.

6. Method of making a cutting tool insert according to claim 1
characterised in that said layer is a cubic (Ti,Si,Me)N phase grown by
cathodic arc evaporation, with a thickness of 0.5 to 10 μm, preferably
1 to 5 μm using a Ti+Si+Me-cathode with a composition expressed as
Ti1-(x+z)SixMez with 0.04<x<0.20, preferably
0.06<x<0.12 and 0<z<0.10, preferably 0.005<z<0.05,
where Me is one or more of the metal elements Y, Hf, Nb, Ta, Mo, W, Mn,
Fe and Zn, preferably Y, Nb, Mo and Fe, and with an evaporation current
between 50 A and 200 A depending on the cathode size, in an Ar+N2
atmosphere, preferably in pure N2 at a total pressure of 0.5 Pa to
7.0 Pa, preferably 1.5 Pa to 5.0 Pa, with a bias between -10 V and -80 V
at a temperature between 400.degree. C. and 700.degree..

7. Method of using a cutting tool inserts according to claim 1 for
machining of stainless steel and super alloys at cutting speeds of 50-400
m/min, preferably 75-300 m/min, with an average feed, per tooth in the
case of milling, of 0.08-0.5 mm, preferably 0.1-0.4 mm depending on
cutting speed and insert geometry.

Description:

BACKGROUND OF THE INVENTION

[0001]The present invention relates to a cutting tool insert comprising of
a body of a hard alloy of cemented carbide, cermet, ceramics, cubic boron
nitride based material or high speed steel and a coating designed to be
used in metal cutting applications generating high temperatures,
particularly machining of super alloys and stainless steel. Said coating
is composed of at least one layer of a thermally stabilized homogeneous
cubic (Ti, Si, Me)N phase, where Me is one or more of the metal elements
Y, Hf, Nb, Ta, Mo, W, Mn, Fe and Zn. The coating is grown by physical
vapour deposition (PVD) and preferably by cathodic arc evaporation.

[0002]TiN has been widely used as hard layer on cutting tools due to its
poor oxidation resistance at elevated temperatures, however, the focus
has shifted towards more complex ternary and quaternary compounds, e.g.
Ti--Al--N, Ti--Al--Si--N and Ti--Cr--Al--N with improved high temperature
performance. For example, Ti--Al--Si--N has been reported as super hard,
H>40 GPa due to a two phase structure consisting of crystalline phase
of NaCl-type in combination with x-ray amorphous Si3N4 or
SiNX.

[0003]EP 1174528 discloses a multilayer-coated cutting tool insert. The
first hard coating film is formed on the insert and a second hard coating
film formed on the first hard coating film. The first hard coating film
comprises one or more of Ti, Al and Cr, and one or more of N, B, C and O.
The second hard coating film comprises Si and one or more metallic
elements selected from the group consisting of metallic elements of
Groups 4, 5 and 6 of the Periodic Table and Al, and one or more
non-metallic elements selected from the group consisting of N, B, C and
O.

[0004]EP 1736565 discloses a cuffing tool insert, solid end mill, or
drill, comprising a body and a coating. The coating is composed of one or
more layers of refractory compounds of which at least one layer comprises
a cubic (Me, Si)X phase, where Me is one or more of the elements Ti, V,
Cr, Zr, Nb, Mo, Hf, Ta and Al, and X is one or more of the elements N, C,
O or B.

[0005]WO 2006/118513 discloses a cutting tool insert, solid end mill or
drill, comprising a body and a coating. The coating is composed of a
cubic C--(Me, Si,) N-phase without coexisting amorphous phase.

[0006]EP 1722009 discloses a cutting tool insert, solid end mill, or
drill, comprising a body and a coating. The coating is composed of one or
more layers of refractory compounds of which at least one layer comprises
a h-Me1Me2X phase, where Me 1 is one or more of the elements V, Cr, Nb,
and Ta and Me2 is one or more of the elements Ti, Zr, Hf, Al, and Si and
X is one or more of the elements N, C, O or B.

[0007]EP 0588350 discloses a hard layer of Ti--Si--N composite material on
a body is carried out by using a source of evaporation possessing a
composition of TiaSib with a in the range of 75- 85 at % and b
15-25at %.

[0008]U.S. Pat. No. 6,033,768 discloses a hard coating consisting of a
layer of a binary, ternary or quaternary TiAl based multicomponent
material comprising nitride or carbonitride with an Al-content of 10 to
70 at %. The layer contains about 0.1 to 4 at % yttrium unevenly
distributed over the entire layer.

[0010]The trends towards dry-work processes for environmental protection,
i.e., metal cutting operation without using cutting fluids (lubricants)
and accelerated machining speed with improved process put even higher
demands on the characteristics of the tool materials due to an increased
tool cutting-edge temperature. In particular, coating stability at high
temperatures, e.g., oxidation- and wear-resistance have become even more
crucial.

[0012]Surprisingly, it has been found that by introducing small amounts of
the metal elements Y, Hf, Nb, Ta, Mo, W, Mn, Fe and Zn in (Ti,Si)N layers
leads to improved high temperature metal cutting properties.

[0017]According to the present invention, there is provided a cutting tool
for machining by chip removal comprising a body of a hard alloy of
cemented carbide, cermet, ceramics, cubic boron nitride based material or
high speed steel onto which a wear and high temperature resistant coating
is deposited composed of at least one cubic structured
(Ti1-(x+z)SixMez)N layer 0.04<x<0.20, preferably
0.06<x<0.12 and 0<z<0.10, preferably 0.005<z<0.05, with
a constant elemental composition throughout the layer, where Me is one or
more of the metal elements Y, Hf, Nb, Ta, Mo, W, Mn, Fe and Zn,
preferably Y, Nb, Mo and Fe. The layer has a thickness of 0.5 to 10 μm
preferably 0.5 to 5 μm.

[0022]The deposition method for the coatings of the present invention is
based on cathodic arc evaporation of an alloyed or composite cathode
under the following conditions; c-(Ti,Si,Me)N layers are grown using
Ti+Si+Me-cathodes with a composition expressed as
Ti1-(x+z)SixMez with 0.04<x<0.20, preferably
0.06<x<0.12 and 0<z<0.10, preferably 0.005<z<0.05,
where Me is one or more of the metal elements Y, Hf, Nb, Ta, Mo, W, Mn,
Fe and Zn, preferably Y, Nb, Mo and Fe. The evaporation current is
between 50 A and 200 A. The layers are grown in an Ar+N2 atmosphere,
preferably in a pure N2 atmosphere at a total pressure of 0.5 Pa to
7.0 Pa, preferably 1.5 Pa to 5.0 Pa. The bias is -10 V to -80 V,
preferably -40 V to -60V. The deposition temperature is between
400° C. and 700° C., preferably between 500 and 600°
C.

[0023]The invention also relates to the use of cutting tool inserts
according to the above for machining of super alloys and stainless steel
at cutting speeds of 50-400 m/min, preferably 75-0 300 m/min, with an
average feed, per tooth in the case of milling, of 0.08-0.5 mm,
preferably 0.1-0.4 mm depending on cutting speed and insert geometry.

[0025]Before deposition, the inserts were cleaned in ultrasonic baths of
an alkali solution and alcohol. The system was evacuated to a pressure of
less than 2.0×10-3 Pa, after which the inserts were sputter
cleaned with Ar ions. (Ti1-xSix)N layers, 0<x<0.20 were
grown by cathodic arc evaporation using cathodes with a composition
varying between pure Ti and

0.75Si0.25, 63 mm in) diameter at 500° C. The layers were
deposited in pure N2 atmosphere at a total pressure of 4 Pa, using a
bias of -50 V and an evaporation current of 60 A to a total thickness of
about 3 μm.

[0026]The composition, x, of the (Ti1-xSix)N layers was
estimated by energy dispersive spectroscopy (EDS) analysis using a LEO
Ultra 55 scanning electron microscope with a Thermo Noran EDS detector
operating at 10 kV. The data were evaluated using a Noran System Six (NSS
ver 2) software.

[0027]X-ray diffraction (XRD) patterns of the as-deposited
(Ti1-xSix)N layers were obtained using Cu K alpha radiation and
a θ-2θconfiguration as function of the Si content (x), see
FIG. 1, corresponding to a NaCl structure of all layers.

[0028]Residual stresses, σ, of the (Ti1-xSix)N layers were
evaluated by XRD measurements using the sin2ψ method (see e.g.
I. C. Noyan, J. B. Cohen, Residual Stress Measurement by Diffraction and
Interpretation, Springer-Verlag, N.Y., 1987). The measurements were
performed using CuKΔ-radiation on the (Ti1-xSix)N
(422)-reflection. The residual stress values were within
-4.0<σ<-2.0 GPa for the different layers as evaluated using a
Possion's ratio of v=0.25 and Young's modulus of E=450 GPa.

[0029]In order to simulate the apparent heat effect that occur during
metal machining, controlled experiments by isothermal heat treatments
were made of the inserts in inert Ar atmosphere at 1000° C. for
120 min.

[0030]Hardness data was estimated by the nanoindentation technique of the
layers after mechanical polishing of the surface using a MTS Nanolndenter
XP system with a Berkovich diamond tip with a maximum tip load of 25 mN.
FIG. 2 shows the hardness (H) of (Ti1-xSix)N layers as a
function of the Si content (x) as obtained at room temperature, before
and after heat treatment at 1000° C. for 2h. Optimum hardness is
obtained for the (Ti1-Six)N layer with x=0.09 corresponding to
the best layer composition for metal machining applications.

[0031]FIG. 3 shows the XRD pattern of a (Ti1-xSix)N layer,
x=0.09, before (I) and after (II) heat treatment at 1000° C. using
CuKa-radiation and a θ-2θconfiguration. The heat treatment
has no effect on the NaCl structure.

EXAMPLE 2

[0032]Grade A: Inserts from example 1 with a (Ti1-xSix)N, x=0.09
composition having a hardness of 39 GPa and a compressive stress level of
-3.1 GPa were used.

EXAMPLE 3

[0033]Grade B: Example 1 was repeated using a
Ti1-(x+z)SixYz cathode, x=0.10 and z=0.03.

[0034]The composition of the resulting (Ti1-(x+z)SixYz)N
layer was x=0.09 and z=0.02. The hardness of the as-deposited layer was
38 GPa and the residual stress level -3.5 GPa.